A membrane distillation, used in processes to prepare pure water or to remove salt from water, serves to remove contaminants. The membrane distillation is performed under a principle that a phase change occurs from the surface of a separation membrane of a hydrophobic polymer, vapor passes through the surface of the separation member through micro holes, and then the transmitted vapor is condensed to be separated.
The membrane distillation has the following advantages.
Firstly, as the membrane distillation is performed by a partial pressure difference between vapor disposed at one side of a separation membrane and vapor disposed at another side thereof, it can be executed at a lower pressure than an ultra filtration or a reverse osmosis. Secondly, the membrane distillation requires no additional pressure. Thirdly, the membrane distillation is effectively used to remove non-volatile ionic materials by separation. Fourthly, the membrane distillation can collect water with a predetermined rate, without being greatly influenced by concentration of contaminants contained in influent water.
The membrane distillation serves to remove contaminants contained in influent water using a hydrophobic polymer separation membrane. A surface tension of a solvent or a solute (hydrophilic material) contained in the influent water is larger than that of the separation membrane. Accordingly, liquid materials are separated from the surface of the separation membrane without passing through pores of the separation membrane. Contaminants undergo a phase change at inlets of the pores formed on the surface of the separation membrane. Then, the contaminants pass through the pores, and are condensed to be separated from the separation membrane. Therefore, such membrane distillation is disadvantageous in effectively removing volatile contaminants.